The porous solid family, of unquestionable significance in everyday life applications as well as industrial applications, still arouses major interest in the research work carried out in the sphere of materials.
Inorganic porous solids have been widely studied in order to increase the opening of their structures so as to facilitate access of the reactants to the active site or departure of the products from this active site.
Since the 1990s, particular interest is taken in hybrid compounds with a mixed organic-inorganic matrix, thus bringing the number of groups that distinguish the porous material types up to 3: inorganic materials, carbon materials and hybrid materials, also referred to as coordination polymers.
These coordination polymers, of which the first ones were described in the 1960s, are the object of an increasing number of publications. In fact, the excitement around these materials has allowed to reach an already advanced structural diversity in a short time (Férey G., L'actualité chimique, January 2007, No. 304). Conceptually, porous hybrid solids with a mixed organic-inorganic matrix are quite similar to porous solids with an inorganic skeleton. Like the latter, they combine chemical entities by giving birth to a porosity. The main difference lies in the nature of these entities. This difference is particularly advantageous and it provides the versatility of this category of solids. In fact, the pore size becomes, through the use of organic ligands, adjustable by means of the length of the carbon chain. The framework which, in the case of inorganic porous materials, could accept only some elements (Si, Al, Ge, Ga, possibly Zn) can, in this case, use all the cations (except the alkaline cations). For these materials, no specific structuring agent is required, the solvent fulfils this function all by itself.
It thus clearly appears that this class of materials allows a multiplicity of structures and, consequently, solids finely suited to the applications they are intended for.
The coordination polymers consist of two elements referred to as connectors and ligands, whose orientation and number of binding sites are determining in the structure of the hybrid material. The diversity of these ligands and connectors gives birth, as already mentioned, to a wide variety of hybrid materials. Other additional auxiliary compounds are also involved in the synthesis: the blockers, counter-ions for example.
What is referred to as ligand is the organic part of the hybrid material. These ligands are, in most cases, di- or tri-carboxylates or pyridine derivatives. Some frequently encountered organic ligands are represented hereafter: bdc=benzene-1,4-dicarboxylate, btc=benzene-1,3,5-tricarboxylate, ndc=naphtalene-2,6-dicarboxylate, bpy=4,4′-bipyridine, hfipbb=4,4′-(hexafluororisopropylidene)-bisbenzoate, cyclam=1,4,8,11-tetraazacyclotetradecane.

The inorganic entity acting as the connector is a single cation, a dimer, a trimer or a tetramer, or a chain, a plane or even a three-dimensional network.
Yaghi and Férey's teams have thus described a large number of new materials (MOF series and MIL series respectively). Many other teams have followed this path and, today, the number of new materials described is in full expansion. Most often, the studies aim to develop ordered structures exhibiting extremely large pore volumes, good thermal stability and adjustable chemical functionalities.
For example, Yaghi et al. describe a series of boron-based structures in patent US-2006/0,154,807 and they show their relevance in the sphere of gas storage. U.S. Pat. No. 7,202,385 by Mueller et al. provides a particularly complete recapitulation of the structures described in the literature and it perfectly illustrates the multitude of materials that already exist today.
T. Loiseau et al. (Chem. Eur. J. 2004, 10, 1373-1382) describe a MIL-53 phase based on aluminium atoms and ligand bdc (benzene-1,4-dicarboxylate). This compound has a three-dimensional structure wherein the one-dimensional inorganic chains with an —Al—O(H)— unit are linked by the deprotonated terephthalic connectors (bdc=O2C—C6H4—CO2). Each aluminium atom is hexacoordinated, two oxygen atoms of the hydroxyl groups being in apical position and four oxygen atoms from four terephthalic connectors being in equatorial position. Furthermore, an organic ligand is linked to four aluminium atoms (two neighbouring aluminium atom pairs). Free terephthalic acid molecules (H2bdc=HO2C—C6H4—CO2H) occupy the “space left vacant by the framework” with a H2bdc/Al ratio of 0.7.
By developing a synthesis mode using another type of metal precursor, based on the element gallium, we have obtained a novel hybrid material with a mixed organic-inorganic matrix.